Intervertebral implant with fixation geometry

ABSTRACT

An intervertebral spacer implant ( 80 ) is provided with a retention mechanism ( 86 ) to help alleviate expulsion and movement of the implant when placed in the spine while providing an implant that is easier to insert in the spine. In one embodiment the retention mechanism comprises a keel on at least one of the inferior or superior faces of the spacer implant preferably extending in an anterior-posterior direction. In another embodiment the implant comprises a spacer ( 84 ) and a plate ( 82 ), the plate comprising a supplemental or alternative retention mechanism. In one embodiment the retention mechanism comprises one or more holes ( 88 ) in the anterior end of the plate. In yet another embodiment, the retention mechanism comprises one or more blades that are in a first position when inserted and are preferably rotated to a second position that engages the superior and inferior vertebrae.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 14/166,979 filed Jan. 29, 2014, which is a continuation of U.S. patent application Ser. No. 12/280,917 filed Jul. 8, 2010, which claims the benefit of International Application No. PCT/US2007/005098 filed Feb. 27, 2007, which claims priority to U.S. Provisional Application Nos. 60/777,732 filed Feb. 27, 2006, 60/777,663 filed Feb. 27, 2006, and 60/838,229 filed Aug. 16, 2006, the entire contents of which are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to intervertebral implants, and, more particularly, to a zero or low profile fusion implant including a retention mechanism that preferably provides integrated fixation geometry.

BACKGROUND OF THE INVENTION

Implants for use in spinal fusion surgery are known in the art. Such implants are used to stabilize and immobilize the spinal segments in the treatment of degenerative disc disease (single and multi-level), spinal stenosis, and failed previous fusions. Some implants use supplemental fixation means, such as a plate and screws, to retain the implant once introduced between two vertebrae.

SUMMARY OF THE INVENTION

The present invention preferably provides for an integrated retention mechanism and spacer implant construction. As such, the implant of the present invention preferably may be inserted using a one-step implantation process, as compared to a two-step process. The present invention preferably allows for implantation of an intervertebral implant and fusion of adjacent vertebrae without the need for additional supplemental fixation means. Preferably, such an implant will minimize dysphasia and irritation of soft tissue, provide sufficient segmental stability in flexion, extension and rotation, provide adequate graft retention, allow for reduced surgery times, minimize surgical trauma, and still allow for additional anterior and/or posterior fixation, if necessary. In one embodiment, the implant may comprise a spacer having a first insertion end portion, a second end portion opposite the first insertion end portion, a first lateral side portion, a second lateral side portion, an upper surface, and a lower surface. The spacer configured and dimensioned for insertion between vertebrae. The Spacer may optionally have one or more keels formed on one of the upper and lower surfaces of the spacer. The keel preferably extends from the first insertion end portion toward the second end portion at least about 50 percent of the distance between the first insertion end portion and the second end portion. Preferably, the keel extends at least about 80 percent, and more preferably 95 percent of the distance between the first insertion end portion and the second end portion.

The keel may have a first insertion end and a second end where the first insertion end may be wedge shaped. The keel may have a plurality of projections that are saw-tooth shaped. The keel may have a first insertion end and a second end portion and the first insertion end of the keel starts at about the first insertion end portion of the implant. The keel may be tapered so that it is higher at its second end relative to the insertion end. The keel preferably has a height of about 1 mm to about 3.5 mm and preferably a width of about 0.5 mm to about 3 mm.

The implant in one embodiment may be formed of an anterior plate secured to the second end portion of the spacer, the plate formed of a different material than the spacer. The plate is preferably formed of a metallic material and the spacer is preferably formed of a non-metallic material. The plate may include at least two through holes, the at least two holes configured to receive screws for securing the implant to adjacent vertebrae and defining first and second hole axes; wherein the first through hole exits through the upper surface and the second through hole exits through the lower surface, and the axes of the first and second through holes form non-zero angles with respect to the upper and lower surfaces.

The plate preferably does not extend beyond the perimeter of the spacer, and more preferably the height of the plate is no more than the height of the spacer at the second end so that the plate does not increase the height profile of the spacer. In this manner the Spacer-plate construct may have a low profile. The through holes in the plate at its outer surface may be generally aligned along a straight line that generally corresponds with the mid-plane of the implant. The spacer and plate preferably are secured together before insertion into the spine. In one embodiment the plate and spacer are connected by at least one dovetail connection, the dovetail connection preferably extends from the upper surface to the lower surface, although the dovetail may extend in a horizontal direction when the spacer is inserted in the spine. The spacer may be solid, or alternatively the spacer may have vertical or horizontal windows or channels. The spacer or plate and spacer construct may have a plurality of projections formed on at least the upper or lower surface, the projections preferably having a height less than the height of the keel. The keel in one embodiment may be formed only on the spacer.

In yet another embodiment the intervertebral implant may comprise a spacer having a first insertion end portion, a second end portion, a first lateral side portion, a second lateral side portion, an upper surface, and a lower surface, wherein the spacer configured and dimensioned for insertion between vertebrae; a plate secured to the first end of the spacer, the plate including at least two through holes defining first and second central hole axes, the at least two holes configured and dimensioned to receive screws for securing the implant to adjacent vertebrae; and at least one keel extending along the upper or lower surface and extending at least 50% of the length of the upper or lower surface between the insertion end portion and the second end portion, wherein the first and second central hole axes form non-zero angles with respect to the upper and lower surfaces of the spacer.

In another embodiment, the intervertebral implant may comprise a spacer having a first insertion end portion, a second end portion, an upper surface, and a lower surface, wherein the spacer is configured and dimensioned for insertion between vertebrae; a Plate secured to the second end portion of the spacer, the plate including one or more blades, preferably two blades, configured and dimensioned to penetrate adjacent vertebrae; and an actuator for causing the one or more blades to move to penetrate adjacent vertebrae. The one or more blades may be configured to rotate from a first position wherein the blades preferably are adjacent the plate to a second position wherein the blades preferably are not adjacent the plate. The blades preferably are configured to provide compression between the vertebrae and the implant as the blades are rotated into the second position. The implant may further comprise a locking mechanism to prevent the blades from rotating back to the first position.

BRIEF DESCRIPTION OF THE DRAWINGS

The intervertebral implant is explained in even greater detail in the following exemplary drawings. The drawings are merely exemplary to illustrate the structure of preferred implants and certain features that may be used singularly or in combination with other features. The invention should not be limited to the embodiments shown.

FIG. 1A is a perspective view of an intervertebral implant according to one embodiment of the present invention positioned between adjacent vertebral bodies;

FIG. 1B is a side view of the implant shown in FIG. 1A;

FIG. 1C is a front view of the implant shown in FIG. 1A;

FIG. 2A is a perspective view of an intervertebral implant employing two retention screws according to another embodiment of the present invention;

FIG. 2B is a top view of the implant shown in FIG. 2A;

FIG. 2C is a side view of the implant shown in FIG. 2A;

FIG. 3A is a perspective view of an intervertebral implant employing three retention screws according to still another embodiment of the present invention;

FIGS. 3B and 3C are front and side views, respectively, of the implant shown in FIG. 3A;

FIGS. 4A and 4B are side and front views, respectively, of the implant shown in FIG. 3A, in position between vertebrae;

FIG. 5A is a perspective view of an intervertebral implant employing four retention screws according to still another embodiment of the present invention;

FIGS. 5B and 5C are front and side views, respectively, of the implant shown in FIG. 5A;

FIG. 5D is a perspective view of two of the implants of FIG. 5A positioned between vertebrae;

FIG. 6A is a perspective view of an intervertebral implant employing top and bottom keels and two retention screws according to still another embodiment of the present invention;

FIGS. 6B and 6C are front and back views, respectively, of the implant shown in FIG. 6A;

FIG. 6D is another perspective view of the implant shown in FIG. 6A;

FIGS. 7A and 7B are top views of an implant employing a dovetail connection between a plate and spacer;

FIG. 8 is a perspective view of an implant employing a dovetail connection between a plate and spacer;

FIG. 9 is a top view of an implant employing two dovetail connections between the plate and spacer;

FIGS. 10A and 10B are top and side views, respectively, of an implant employing a dovetail connection running horizontally between the plate and spacer;

FIGS. 11A and 12A are top views of implants employing a plate and spacer where the plate sides wrap around a portion of the spacer;

FIGS. 11B and 12B are perspective views of the plates of FIGS. 11A and 12A, respectively;

FIG. 13 is a top view of an implant employing a “jigsaw puzzle” connection between the plate and spacer;

FIG. 14A is a perspective view of an implant wherein the plate and spacer are integrally formed with one another;

FIGS. 14B-14E are rear, front, side and top views of the implant depicted in FIG. 14A;

FIG. 14F is a side view of the implant depicted in FIG. 14A, in position between adjacent vertebrae;

FIG. 15A is a perspective view of an intervertebral implant employing top and bottom keels according to yet another embodiment of the present invention;

FIGS. 15B-15D are front, side and top views, respectively, of the implant depicted in FIG. 15A;

FIG. 16A is a perspective view of an intervertebral implant employing top and bottom keels according to yet another embodiment of the present invention;

FIG. 16B is a side view of the implant depicted in FIG. 16A;

FIG. 17A is a perspective view of an intervertebral implant employing top and bottom keels according to yet another embodiment of the present invention;

FIG. 17B is a side view of the implant depicted in FIG. 17A;

FIG. 18 is a perspective view of an intervertebral implant employing top and bottom keels according to yet another embodiment of the present invention; and

FIG. 19 is a perspective view of an intervertebral implant employing top and bottom keels according to still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally to FIGS. 1A, 1B and 1C, an intervertebral implant 10 according to an embodiment of the present invention is illustrated. As known in the art, the implant 10 is inserted between adjacent vertebra (shown schematically as 50 in FIGS. 1A-1C) of the spinal column. In this embodiment, the implant includes a plate 11 and a graft/spacer 12 combined with a retention mechanism 14. As shown, implant 10 includes an upper surface 16 and a lower surface 18, which may taper, be curved, arcuate or flat as desired or to conform to the end plates of the vertebrae and the intervertebral space. As shown, upper and lower surfaces 16, 18 may include a series of teeth or similar projections 19 to aid in securing the implant to the vertebral endplates.

In addition, the implant includes retention mechanism 14 which preferably has two wedge-shaped blades 20, although more or less blades 20 may be included. Following implantation between vertebrae, retention mechanism 14 is torsionally driven into vertebral bodies 50 and rotationally locked. More particularly, wedge-shaped blades 20 may be rotated to engage, penetrate or cut through the endplates of vertebral bodies 50 to hold implant 10 in position. Wedges 20 preferably are pointed and shaped to facilitate penetrating the end plates. Preferably, retention mechanism has a recess 15 or projection (not shown) to receive a tool to rotate retention mechanism 14 relative to plate 11 and spacer 12. Preferably, retention mechanism 14 includes a locking mechanism 23 to prevent rotation of blades 20 or otherwise lock the position of the blades 20 in the vertebrae. Retention mechanism 14 may have a hub (not shown) that projects into and is held in a cavity (not shown) in the plate 11. The hub is held or retained in the cavity, but may rotate relative to the plate. Recess 15 is preferably star-shaped and formed in the hub.

In the insertion position the pointed tips 17 on the blades 20 are directed toward the vertebrae. In the embodiment shown, one pointed tip 17 is directed toward the superior vertebrae and one pointed tip 17 is directed toward the inferior vertebrae. After the implant 10 is positioned between the vertebrae, the retention mechanism is rotated clockwise so that the pointed tips 17 preferably are directed in the lateral/medial direction. In the preferred embodiment, the retention mechanism is rotated approximately 90°, although the retention mechanism may be rotated by more or less angular amounts. As the blades are rotated they engage, penetrate into, or cut through the vertebrae. The blades are preferably wedge-shaped and preferably compress the adjacent vertebrae together or towards one another as they are rotated.

Implant 10 may also include openings 22 for additional fixation screws, if necessary. Openings 22 may also permit screws that permit the plate 11 to be attached to the spacer 12. Both plate 11 and graft/spacer 12 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone or any other suitable, biocompatible material. Preferably plate 11 and retention mechanism 14 are formed of metal or metal alloy and the spacer is formed of PEEK or other polymer, or alternatively bone or ceramic or radiolucent biocompatible material. Screws not shown) may be formed of titanium, titanium alloy or stainless steel. Graft/spacer 12 may include one or more openings (not shown) designed to receive bone graft material.

Reference is now made to FIGS. 2A, 2B and 2C, which show an intervertebral implant 30 according to another embodiment of the present invention. Implant 30 includes a plate 32 and a spacer/graft 34. As shown, in this embodiment, the retention mechanism is provided by screws that provide opposing screw fixation. In other words, for example, one screw diverges outward such that it is secured into an upper or superior vertebra and another screw diverges outward from the implant such that it is secured in a lower or inferior vertebra so that opposing forces act on the plate and/or vertebrae. A pair of holes or openings 36 accept two screws 38, which penetrate the vertebral bodies and secure the implant in place. One of holes 36 is angled upward toward the upper or superior vertebrae, and the other hole 36 is angled downward toward the lower or inferior vertebrae, such that holes 36 form an angle with respect to the upper and lower surfaces 26, 28 of the implant 30. As shown best in FIG. 2C, holes 36 form an angle α with respect to the upper and lower surfaces of the implant, where α may range between 20° and 50°, and preferably ranges between 30° and 45°. Angle α may be the same for all holes 36 or may be different for each hole. After the implant is placed between adjacent vertebrae, screws 38 are inserted through the holes 36 in plate 32 to penetrate the vertebrae and hold the implant in position, i.e., one screw is inserted into the upper vertebrae and the other is inserted into the lower vertebrae. As with the previous embodiment, upper and/or lower surfaces 26, 28 of the implant may include a series of teeth 19, or other similar projections, to aid in securing the implant to the vertebral endplates. Both plate 32 and graft/spacer 34 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone or any other suitable, biocompatible material, or any combination thereof. Screws 38 may be formed of titanium, titanium alloy or stainless steel. Graft/spacer 34 may include one or more openings 33 designed to receive bone graft material.

Plate 32 is preferably formed of metal or metal alloy and the spacer 34 is preferably formed of PEEK or other polymer, or bone (allograft) or ceramic or other radiolucent, biocompatible material. The plate 32 preferably is of the same height or less than the height of the spacer 12 so the implant has a low profile. The plate is preferably connected to the spacer 12 before the implant 10 is implanted. Preferably the holes 36 are formed substantially along a single substantially horizontal line 5 or plane in the plates. The line or plane along which the holes 36 are formed in the outer surface of the plate 32 is preferably substantially the mid-plane 5 of the implant. In the embodiment of FIGS. 2A-2C, the exit openings 37, 39 for the screw holes 36 are formed in the plate. The plate 32 is preferably connected to the spacer 34 by a dovetail joint 31 that requires the plate 32 to the slide vertically relative to the spacer 34.

Reference is now made to FIGS. 3A, 3B and 3C, which show an intervertebral implant 40 according to still another embodiment of the present invention. As with the embodiment shown in FIG. 2A, implant 40 includes a plate 42 and a spacer/graft 44, and the retention mechanism is provided by screws that provide opposing screw fixation. As shown, three holes 46 accept three fixation screws 48, which penetrate the vertebral bodies and secure the implant in place, as shown in FIGS. 4A and 4B. As shown best in FIG. 3C, holes 46 form an angle α with respect to the upper and lower surfaces 41, 45 of the implant, where α may range between 20° and 50°, and preferably ranges between 30° and 45°. Angle α may be the same for all holes 46 or may be different for each hole. After the implant is placed between adjacent vertebrae, screws 48 are inserted through the holes 46 in plate 42 to penetrate the vertebrae and hold the implant in position. In this embodiment, one screw 48 penetrates the upper vertebrae and two screws 48 penetrate the lower vertebrae. As with the previous embodiment, upper and/or lower surfaces 41, 45 of the implant 40 may include a series of teeth 19, or other similar projections, to aid in securing the implant to the vertebral endplates. Both plate 42 and graft/spacer 44 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone or any other suitable, biocompatible material, or any combination thereof. Screws 48 may be formed of titanium, titanium alloy or stainless steel. Graft/spacer 44 may include one or more openings 43 designed to receive bone graft material.

Plate 42 is preferably formed of metal or metal alloy and spacer 44 is preferably formed of PEEK, other polymer, bone, ceramic or other radiolucent, biocompatible material. The plate 32 preferably is the same height or less than the height of the spacer. As with implant 30, plate 42 is preferably connected to spacer 44 prior to implantation and holes 46 are preferably formed substantially along a substantially horizontal line in the outer end surface 43 of the plate 42 at an angle α so that at least two fixation screws are directed in opposed directions, one toward the superior vertebrae and one toward the inferior vertebrae. In the embodiment of FIGS. 3A-3C, the exit openings 47, 49 in the superior and inferior surfaces for the screws are preferably formed at the junction of the plate and spacer, or in the spacer. Alternatively, like the embodiment of FIGS. 2A-2C, the exit openings 47, 49 may be formed entirely with in the plate 42.

The superior surface, the inferior surface or both surfaces of the spacer and the implant construct may have a curved surface to help provide the proper shape to the spine. The particular surface shape and curvature, or taper in the anterior-posterior direction as well as between the lateral side surfaces will depend upon the location the spacer is intended to be inserted. The shape of the perimeter of the spacer shown in FIGS. 2-14 are generally for cervical applications and the spacer may have an alternative shape, such as that illustrated by the perimetral shape of FIG. 15 for other locations such as in the lumbar area of the spine.

Reference is now made to FIGS. 5A, 5B and 5C, which show an intervertebral implant 60 according to still another embodiment of the present invention. As with the embodiment shown in FIG. 3A, implant 60 includes a plate 62 and a spacer/graft 64, and the retention mechanism is provided by screws which provide opposing screw fixation. As shown, four holes 66 accept four fixation screws 68, which penetrate the vertebral bodies and secure the implant 60 in place, as shown in FIG. 5D. As shown best in FIG. 5C, holes 66 form an angle α with respect to the upper and lower surfaces 61, 65 of the implant 60, where α may range between 20° and 50°, and preferably ranges between 30° and 45°. Angle α may be the same for all holes 66 or may be different for each hole. After the implant is placed between adjacent vertebrae, screws 68 are inserted through the holes 66 in plate 62 to penetrate the vertebrae and hold the implant in position. In this embodiment, the two inner screws 68 penetrate the upper vertebrae and the two outer screws 68 penetrate the lower vertebrae. As with the previous embodiment, upper and/or lower surfaces of the implant may include a series of teeth 19, or other similar projections, to aid in securing the implant to the vertebral endplates. Both plate 62 and graft/spacer 64 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof. Screws 68 may be formed of titanium, titanium alloy or stainless steel. Graft/spacer 64 may include one or more openings 63 designed to receive bone graft material. Preferably the plate 62 is formed of a metal or metal alloy and the spacer 64 is formed of PEEK, other polymer, bone allograft, ceramic or other radiolucent biocompatible material. The holes 66 are formed in the outer surface 3 of the end wall of the plate 62 substantially along a horizontal line or plane at an angle α.

The screw holes 66 in the plate 62 preferably are directed outward from the center of the implant, preferably at an angle .theta. The screw hole openings and configurations, as well as the screws may have the configuration and construction and materials described in US2005/0177236 which is incorporated by reference herein in its entirety. The screws inserted in the embodiments of FIGS. 5A-5C do not intersect a vertical plane cutting the implant 60 into two substantial halves. The screws, and the screw holes, in the embodiment of FIGS. 5A-5C on the left side, one of which extends in the superior direction and the other which extends in the inferior direction may extend laterally outward from the center plane at different angles .theta., or at the same angle .theta. Preferably the two outermost holes 66 in the implant 60 extend toward the inferior vertebrae while the two inner screw holes 66 extend toward the superior vertebrae.

FIGS. 6A-D show an intervertebral implant 80 according to yet another embodiment of the present invention. As with the embodiments shown in FIGS. 2A, 3A and 5A, implant 80 includes a plate 82 and a spacer/graft 84. However, in this embodiment, the retention mechanism is provided by a combination of opposing keels 86 on the top and bottom surfaces 81, 85 and screws providing opposing screw fixation. The upper and lower keels 86 provide additional additive resistance to torsion or rotation of the implant. As shown, in addition to upper and lower keels 86, a pair of holes 88 accept two fixation screws 89, which penetrate the vertebral bodies and secure the implant in place. As with previous embodiments, holes 88 form an angle α with respect to the upper and lower surfaces of the implant, where α may range between 20° and 50°, and preferably ranges between 30° and 45°. Angle α may be the same for all holes 88 or may be different for each hole.

After the implant is placed between adjacent vertebrae, screws 89 are inserted through the holes 88 in plate 82 to penetrate the vertebrae and aid in holding the implant in position. As with previous embodiments, upper and/or lower surfaces 81, 85 of the implant 80 may include a series of teeth 19, or other similar projections, to aid in securing the implant to the vertebral endplates. Preferably, the keel 86 is at least as high as the teeth or protrusions 19. The keel preferably may have a height of about 1 mm to about 3.5 mm. The keel 86 may have the shape shown in FIG. 86, although it may have the shapes shown in FIGS. 15-19, or other shapes. The keel 86 preferably extends in the anterior-posterior direction. The leading end 85 of the keel may be pointed or tapered so that it gets wider from the posterior end 83 to the anterior end 83. The keel preferably may be about 0.5 mm to about 3.0 mm wide. The keel may also get higher as it extends from the posterior end to the anterior end. The taper in the height and width may permit easier insertion of the implant.

The keel 86 may only extend along the spacer as shown, or may extend along the spacer 84 and plate 82. The length of the keel may be, and preferably is, greater than the width of the keel. The length of the keel 86 is preferably greater than about 50 percent of the length of the implant 80 in the posterior to anterior direction and in some embodiments preferably greater than about 80 to about 95 percent of the length of the implant 80 in the anterior-posterior direction.

Both plate 82 and graft/spacer 84 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof, while screws 89 may be formed of titanium, titanium alloy or stainless steel. Graft/spacer 84 may include one or more openings (not shown) designed to receive bone graft material. As with the earlier embodiment the plate is preferably a different material than the spacer, and the plate is preferably a metallic material whereas the spacer is a non-metallic material. A preferred embodiment for the implants 10, 30, 40, 60 and 80 may include a titanium alloy for the plate and an allograft for the spacer.

FIGS. 7A-13 depict various attachment mechanisms for attaching the plate and spacer of the implant together. The attachment mechanisms between spacer and plate are not limited to the mechanisms depicted. Various figures depict two or three holes of the retention feature of the implant. It should be noted that the number of holes two, three, or four of the retention feature of the implant is not limited by the type of attachment mechanism between the spacer and plate.

FIGS. 7A and B depict a top view of dovetail connection 1010 between plate 1100 and spacer 1200 (These figures do not depict the holes of the retention feature so as to more clearly illustrate the dovetail connection 1010). The dovetail connection 1010 may extend from the upper surface to the lower surface of the implant 1000. As shown in these figures, the thickness T of the plate 1100 may vary depending on the application. Representative values for T include about 5 mm to about 7 mm. Furthermore, the size of the dovetail connection 1010 may also vary in size, both in length and in width. As shown in FIGS. 7A and B, the male dovetail connector 1011 is formed as part of the plate 1100 while the female connector 1012 is formed on the spacer 1200. It is contemplated that the female connector may be formed on the plate and the male connector may be formed on the spacer. FIG. 8 is a perspective view of an implant 1000 with a dovetail connection 1010 between the plate 1100 and spacer 1200. In this figure, the implant 1000 includes three holes 1110 similar to the embodiment depicted in FIGS. 3A-4B.

FIG. 9 depicts an implant 1000 having two dovetail connections 1010, 1020 between the spacer 1200 and plate 1100. In this embodiment, the dovetail connections 1010, 1020 may extend between the upper surface and lower surface of the implant. It is contemplated that the dovetail connections may extend from one lateral side 1001 of the implant 1000 to the other lateral side 1002. FIGS. 10A and 10B depict such a dovetail connection between the plate 1100 and spacer 1200.

FIGS. 11 and 12 depict further embodiments of the connection between the plate 1100 and spacer 1200. In these embodiments, the sides 1110 of the plate 1100 “wrap” around the proximal end (front) of the spacer 1200. The length or thickness of the sides 1110 of the plate 1100 may vary, as depicted in the two figures, depending on the application.

FIG. 13 depicts another embodiment of the connection between the plate 1100 and spacer 1200. In this embodiment, the connection between the plate and spacer is a “jigsaw puzzle” connection 1040. The shape of the “jigsaw puzzle” connection 1040 may vary depending on the application. As with the other embodiments discussed above, the male and female connectors of the connection may be formed on the spacer 1200 or plate 1100, depending on the application.

FIGS. 14A-F depict a cervical spacer-plate implant 2000. FIG. 14A is a perspective view of the implant 2000, whereas FIGS. 14B-E are various plane views of the implant. In this embodiment, the plate 2020 and spacer 2010 are integrally formed. The implant 2000 may have an arcuate front face 2100, whereas the end face 2200 of the implant may be plane or arcuate. The implant 2000 may also have arcuate first and second lateral surfaces 2300, 2400, respectively, and an upper surface and a lower surface 2500, 2600. The upper surface 2500 may be arcuate to conform to the contour of the endplate of the upper vertebra. The lower surface 2600 is generally a substantially flat planar surface. The distance between the upper and lower surfaces 2500, 2600 at the front face 2100 may be greater than at the end face 2200. The front face 2100 may be wider than the end face 2200 such that the first and second lateral surfaces 2300, 2400, connected to the front and end faces 2100, 2200 are further apart from each other at the front face than at the end face. The implant 2000 may include one or more openings designed to receive bone graft material. In particular, one or more vertical windows/channels 2700 may extend through the implant from the lower surface 2600 to the upper surface 2500. In some embodiments, the implant 2000 may also have one or more horizontal channels 2800 extending from the first lateral surface 2300 to the second lateral surface 2400, and/or from the front face 2100 to the end face 2200.

The front face 2100 has a height greater than the height of the spacer 2010 to accommodate a retention feature provided by opposing screw fixation. As shown, four holes 2900 accept four fixation screws 2950 which penetrate the vertebral bodies 50 and secure the implant 2000 in place, as shown in FIG. 14F. The holes 2900 form an angle α with respect to the upper and lower surfaces 2500, 2600 of the implant 2000, where the angle may range between 20° and 50°, and preferably ranges between 30° and 45°. The angle α may be the same for all holes or may be different for each hole. After the implant 2000 is placed between adjacent vertebrae 50, screws 2950 are inserted through the holes 2900 to penetrate the vertebrae and hold the implant in position. As with previous embodiments, the upper and/or lower surfaces 2500, 2600 of the implant may include a series of teeth 19, or similar projections, to aid in securing the implant to the vertebral endplates. It is also contemplated that the upper and/or lower surfaces 2500, 2600 may be smooth, having ridges that run laterally with respect to the spacer 2010, or ridges running from the front face 2100 to the end face 2200. The implant 2000 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof, while screws 2950 may be formed of titanium, titanium alloy or stainless steel.

It should be noted that the screw holes provided in the plates of the embodiments of FIGS. 2-14 may be threaded or smooth, and the screw inserted through the plate may have a head that also may be threaded or smooth. In the embodiment where the screw holes are threaded the heads of the screws are also preferably threaded so that the screw will lock with the plate forming a relatively rigid construct.

Reference is now made to FIGS. 15A-D, which shows an intervertebral implant 70 according to still another preferred embodiment of the present invention. FIG. 15A is a perspective view of the implant, while FIGS. 15B-D are plane views of the implant. In this embodiment, a pair of opposing dovetail keels 72 on the upper and lower surfaces 71, 73 of the implant 70 provide the retention feature. The implant may have arcuate anterior and posterior faces, both curved in the same direction to form a generally kidney bean shape. The keel is generally centrally located and preferably extends about 50 percent the length of the superior and inferior surfaces in an anterior to posterior direction, and more preferably about 80 to about 95 percent of the length in the anterior to posterior direction. The dovetail shape of the keel 72 preferably assists in retaining the implant 100 in position and helps to prevent expulsion of the implant. In particular, the dovetail shape will help to retain contact between the upper and lower surface of the implant and the end plates of the vertebrae. The dovetail shape may also be configured to provide compression. The shape of the implant 70 is generally preferred for the lumbar region of the spine.

No additional plates or screws may be necessary. Implant 70 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof. Implant 70 may include one or more openings designed to receive bone graft material. In particular, one or more vertical windows/channels 75 may extend through the implant 70 from the lower surface 73 to the upper surface 71. In some embodiments, the implant 70 may also have one or more horizontal channels 74 extending from a first lateral surface 77 to a second lateral surface 78, and/or from the front face 79 a to the end face 79 b.

The implant 100, shown in FIGS. 16A and B, may have arcuate anterior and posterior faces 110, 112, respectively. Superior and inferior faces, 114, 116, respectively, may have projections or teeth 118 for engaging the adjacent vertebrae and aiding in securing the implant 100 in the disc space. The projections 118 may be pyramidal in shape as shown, or may have other shapes. One or more vertical windows/channels 124, designed to receive bone graft material, may extend through the implant 100 from the inferior face 116 to the superior face 114. In some embodiments, the implant 100 may also have one or more horizontal channels 126 designed to receive bone graft material. The implant also has longitudinal sides 102, 103, wherein a first longitudinal side's 102 height may be, and preferably is, less than the height of the second longitudinal side 103.

The implant 100 further may have a retention feature comprising a first fixation member 105 projecting from the superior face 114 and a second fixation member 115 projecting from the inferior face 116. The first and second fixation members 105, 115 resemble a “keel” such that the keel is oriented from the anterior face 110 to the posterior face 112. The length of the keel may be, and preferably is, greater than the width of the keel, and whose length preferably is 80 to 95 percent of the width of the superior and inferior faces 114, 116. The first and second fixation members 105, 115 have a height greater than the height of the projections or teeth 118. The first and second fixation members 105, 115 may have projections 106, such as in the form of a saw-tooth, for engaging the adjacent vertebrae and aiding in securing the implant 100 in the disc space without the need for supplemental fixation means. The saw-tooth shape of the projections allows the implant to be inserted while requiring a larger force for the implant to be removed from between vertebrae. The keel also helps prevent rotation or turning of the implant. No additional plates or screws may be necessary to retain the implant between two vertebrae. Implant 100 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof.

FIGS. 17A and B depict another embodiment of the implant 200. The implant 100 may have end faces 210, 212, respectively. The end faces 210, 212 may be substantially flat or arcuate shaped. Face 210 may have a greater length than face 212. The implant also may have arcuate first and second longitudinal surfaces 202, 203, respectively, and an inferior face 216 and a superior face 214. One or more vertical windows/channels 224 may extend through the implant 200 from the inferior face 216 to the superior face 214. Additional vertical channels 230, extending from the inferior face 216 to the superior face 214 may be positioned on the perimeter of the superior and inferior faces 214, 216. In some embodiments, the implant 200 may also have one or more horizontal channels 226. The height of the first face 210 may be greater than the height of the second face 212.

The implant 200 further may have a retention feature comprising a first fixation member 205 projecting from the superior surface 214 and a second fixation member 215 projecting from the inferior surface 216. The first and second fixation members 205, 215 resemble a “keel” such that the keel is oriented from face 210 to face 212. The length of the keel may be, and preferably is, greater than the width of the keel, and whose length preferably is 80 to 95 percent of the length of the superior and inferior faces 214, 216. The first and second fixation members 205, 215 may have projections 206, such as in the form of a saw-tooth, for engaging the adjacent vertebrae and aiding in securing the implant 200 in the disc space, preferably without the need for supplemental fixation means. No additional plate or screws may be necessary to retain the implant between two vertebrae. Implant 200 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof.

The intervertebral implant 300, shown in FIG. 18, has arcuate end faces 310, 312, respectively. Superior and inferior faces, 314, 316, respectively, which may be curved and may have projections or teeth 318 for engaging the adjacent vertebrae and aiding in securing the implant 300 in the disc space. The projections 318 may be pyramidal in shape. The implant also has longitudinal sides 302, 303. The intervertebral implant 300 of this embodiment differs from the implant 100 in that intervertebral implant 300 has no horizontal or vertical channels, such that superior and inferior faces 314, 316 and longitudinal surfaces 302, 303 has no openings.

The implant 300 further has a retention feature comprising a first fixation member 305 projecting from the superior face 314 and a second fixation member 315 projecting from the inferior face 316. The first and second fixation members 305, 315 resemble a “keel” such that the keel is oriented from front face 310 to end face 312. The length of the keel may be, and preferably is, greater than the width of the keel, and whose length is 80 to 95 percent of the width of the superior and inferior faces 314, 316. The first and second fixation members 305, 315 have a height greater than the height of the projections or teeth 318. The first and second fixation members 305, 315 may have projections 306, such as in the form of a saw-tooth, for engaging the adjacent vertebrae and aiding in securing the implant 300 in the disc space, preferably without the need for supplemental fixation means. No additional plate or screws may be necessary to retain the implant between two vertebrae. Implant 300 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof.

FIG. 19 depicts yet another embodiment of an implant 400 having first and second fixation members 405, 415 that resemble a “keel” such that the keel is oriented from front face 410 to end face 412. The first and second fixation members 405, 415 may have generally parallel side walls 416, 417 from the front towards the rear or end of the fixation members 405, 415. The side walls 416, 417 of the first and second fixation members 405, 415 near the end of the keel may be angled towards each other forming a wedge 418 at the end of the members 405, 415. The wedge 418 may allow for easier insertion between two vertebrae 50. The length of the keel may be, and preferably is, greater than the width of the keel, and whose length is 80 to 95 percent of the width of the superior and inferior faces 414, 416. The first and second fixation members 405, 415 have a height greater than the height of the projections or teeth 418. The first and second fixation members 405, 415 may include a recess 422. The recess 422 may be sized to fit an insertion tool (not shown), such that the front 420 of the first and second fixation member 405, 415 have an opening allowing the insertion tool to grip the implant 400 for insertion between two vertebrae. Implant 400 may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone, or any other suitable, biocompatible material, or any combination thereof.

The implants described herein are generally sized and configured for anterior insertion, although different configurations may be possible for posterior approaches. In addition to the features shown the implants, spacers, and plate/spacer constructs may have threaded holes, slots or channels to mate with instruments to facilitate holding and inserting the implants.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention.

It will be appreciated by those skilled in the art that various modifications and alterations of the invention can be made without departing from the broad scope of the appended claims. Some of these have been discussed above and others will be apparent to those skilled in the art. For example, the present invention may be employed in different sections of the spinal column, including, but not limited to, the cervical area. 

What is claimed is:
 1. An intervertebral implant comprising: a spacer having upper and lower surfaces configured to face a superior vertebra and an inferior vertebra, respectively, wherein the upper and lower surfaces are opposite each other along a transverse direction; and a dovetail shaped keel that extends out from the upper surface, the keel having first and second side surfaces and an end surface that extends between the first and second side surfaces at a location spaced from the upper surface, wherein the first and second side surfaces flare away from each other as they extend from the upper surface to the end surface, and the dovetail shaped keel assists in maintaining contact between the upper surface of the spacer and an endplate of the vertebra, wherein the implant defines a front face and an end face opposite the front face along an anterior-posterior direction that is perpendicular to the transverse direction, the keel extends from the front face to the end face, and a tapered leading end of the keel is defined by each of the first and second side surfaces tapered toward the other of the first and second side surfaces to a blunt tip as the first and second side surfaces extend in the anterior-posterior direction to the end face, such that the keel defines a first width and a second width that is greater than the first width, wherein the first width is defined as a first distance from the first side surface to the second side surface along a lateral direction that is perpendicular to each of the anterior-posterior direction and the transverse direction 1) at the tapered leading end of the keel, and 2) in a plane that is defined by the anterior-posterior direction and the lateral direction, wherein the second width is defined as a second distance from the first side surface to the second side surface along the lateral direction 1) at a keel location between the tapered leading end and the front face, and 2) in the plane, wherein the keel has a height from the upper surface to the end surface, and the height at the tapered leading end is constant and equal to the height at the keel location, wherein the upper surface defines a continuous and uninterrupted path from the first side surface to the second side surface, and wherein the height is constant from the front face to the end face and the second width is constant from the front face to the tapered leading end.
 2. The intervertebral implant as recited in claim 1, wherein the dovetail shaped keel is a first dovetail shaped keel, and the implant further comprises a second dovetail shaped keel that extends from the lower surface, the second dovetail shaped keel having third and fourth side surfaces and a second end surface that extends from the third side surface to the fourth side surfaces at a respective location spaced from the lower surface, wherein the third and fourth side surfaces flare away from each other as they extend from the lower surface to the second end surface, and a leading end of the second dovetail shaped keel is tapered as it extends along the anterior-posterior direction to the end face.
 3. The intervertebral implant as recited in claim 2, wherein the end surface of the first keel extends continuously from the first side surface to the second side surface, and the second end surface extends continuously from the third side surface to the fourth side surface.
 4. The intervertebral implant as recited in claim 2, wherein the upper and lower surfaces are spaced from each other along the transverse direction, the first and second keels extend out from the upper and lower surfaces, respectively, along the transverse direction, are elongate along anterior-posterior direction, and are centrally located on the upper and lower surfaces, respectively, with respect to the lateral direction that is perpendicular to each of the transverse and anterior-posterior directions.
 5. The intervertebral implant as recited in claim 4, wherein the first and second side surfaces are opposite each other along the lateral direction, and the third and fourth side surfaces are opposite each other along the lateral direction.
 6. The intervertebral implant as recited in claim 2, wherein the front face and the end face are arcuate.
 7. The intervertebral implant as recited in claim 6, wherein the front face and the end face are curved in the same direction.
 8. The intervertebral implant as recited in claim 7, wherein the implant is kidney bean shaped.
 9. The intervertebral implant as recited in claim 2, wherein the implant defines a vertical channel that extends from upper surface to the lower surface, the vertical channel configured to receive bone graft.
 10. The intervertebral implant as recited in claim 9, wherein the implant defines first and second vertical channels that are configured to receive bone graft and extend from upper surface to the lower surface, and the first and second vertical channels are on opposite sides of the first and second keels.
 11. The intervertebral implant as recited in claim 2, wherein the implant defines a horizontal channel that extends from the front face to the end face.
 12. The intervertebral implant as recited in claim 2, wherein the first and second keels extend out from the upper and lower surfaces, respectively, along the transverse direction, are elongate along the anterior-posterior direction, the implant defines first and second lateral side surfaces that are opposite each other along the lateral direction that is perpendicular to each of the transverse direction and the anterior-posterior direction, and the implant defines a horizontal channel that extends from the first lateral side surface to the second lateral side surface.
 13. The intervertebral implant as recited in claim 2, wherein the implant is a one-piece body.
 14. The intervertebral implant as recited in claim 13, wherein the implant is devoid of screws.
 15. The intervertebral implant as recited in claim 2, wherein the first keel is the only keel of the implant that extends from the upper surface, and the second keel is the only keel of the implant that extends from the lower surface.
 16. The intervertebral implant as recited in claim 1, wherein the implant is devoid of screws.
 17. The intervertebral implant as recited in claim 1, wherein the implant comprises PEEK.
 18. The intervertebral implant as recited in claim 1, wherein the implant comprises allograft.
 19. The intervertebral implant as recited in claim 1, wherein the first and second side surfaces converge toward each other in the plane at the tapered leading end as they extend toward the end face.
 20. The intervertebral implant as recited in claim 19, wherein one of the first and second sides defines a straight line from the upper surface to the end surface.
 21. The intervertebral implant as recited in claim 20, wherein the first and second sides extend parallel to each other from the front face to the tapered leading end. 